| Do you know of any examples of devices that do even 4 levels? Every
| device I know of that adjusts to ambient light just has a two-stage
| switch between light and dark. For example, that's what google maps
| does.
You're right, I don't know any application which use 4 levels.
Meanwhile, in his experiment, Microsoft concluded 3 levels were useful for
light-aware applications: dim, normal and washed [1]. Even if it's very
difficult to find light-aware apps these days, this doesn't mean that this
is not useful, just that nobody cared to implement that. Meanwhile, it's
easy to find independent reviewers giving the advice to increase font size
in direct sunlight (so users do take action in that case) [2] and you can
find designers at stackoverflow giving tips such as using high contrast and
making the font bolder on mobile website likely used outdoor [3].
I believe that when the screen's brightness can't be increased further to
compensate decently the ambient light conditions, the designer should be
able to take actions to make things better the same way it does when the
ambient light is too low (night mode).
[1] http://www.techmynd.com/ipad-direct-sunlight-exposure/
[2]
http://www.istartedsomething.com/20081030/windows-7-and-light-sensors-let-there-be-light/
[3]
http://ux.stackexchange.com/questions/15887/how-does-use-in-bright-sunlight-affect-how-a-web-site-should-be-designed